Starches molecular mobility

Choi, S.-G. and Kerr, W.L. 2003a. H NMR studies of molecular mobility in wheat starch. Food Res. Int. 36, 341-348. 

Starch annealing involves heating starches with sufficient hydration below their Tq to facilitate molecular mobility (Tester et ah, 2001). Annealing is defined as "a physical treatment that involves incubation of starch granules in excess (>60% w/w) or at intermediate (40-55% w/w) water content during a certain period of time at a temperature above the glass... 

Kulik, A. S., Chris de Costa, J. R., Haverkamp, J. (1994). Water organization and molecular mobility in maize starch investigated by two-dimensional solid-state NMR. Journal of Agricultural and Food Chemistry, 42, 2803-2807. 

C in all cases, the commonly used frozen storage conditions (approximately — 18°C) would be located above the Tg temperatures thus systems stored at this temperature would be at the rubbery state and would have more molecular mobility. In this situation, deteriorative phenomena depending on diffusion could occur. As amylopectin and amylose retrogradation are crystallization phenomena occurring in starch systems, they were studied in the present work as examples of deteriorative changes. As observed in Table 18.1, values foimd for the onset temperature (T p varied between... 

The addition of sucrose shifted T g towards lower values (onset between — 23 and — 22°C, depending on the system). Thus, commercial storage temperatures (= — 18°C) lie above Tg in starch-sucrose systems, allowing molecular mobility this fact led to amylose and amylopectin retrogradation... 

The inhibition of molecular mobility at low water content was better reflected in the restrictions for protein denaturation, starch gelatinization, and water crystallization. Starch gelatinization was only observed in fully hydrated systems. The increase in water content was also reflected on the increased extent of protein denaturation and the decrease of the temperatures at which this transition occurred. Freezable water was detected in samples of... 

Molecular Mobility in Glassy Starch Influence of Hydration and Sucrose... 

Molecular mobility of gelatinized starch was considered through the effect of water and sucrose contents on structural relaxation and viscoelastic behavior. 

Starch hydration, water mobility, and the effect of chemical modification on molecular mobility of starch have also been studied using LR NMR. 

For the unblended PIS (100 0) and PVOH (0 100), the Tj values are, respectively, 4.2 and 5.9 ms, which is sufficiently different to observe their variations upon blending in different proportions. It can be distinguished that the values decreased in the plasticized starch (100 0) compared to that of the raw starch (5.2 ms), undoubtedly due to the increased molecular mobility of the amylose chains after thermomechanical processing in the presence of a plasticizer. A similar relaxation behavior of wheat proteins after plasticization by glycerol has been previously observed [15]. The relaxation behavior of PVOH was not similarly affected after processing, in the neat PVOH being 5.5 ms. 

However, the of the PVOH component was lowered by increasing the amount of starch in the blend. Whilst this depression of the of PVOH is an indication of mixing, the fact that no averaging takes place between the of PVOH and starch is a sign that their miscibility is limited, most likely to local regions such as interfaces. It should also be noted that the intrinsic relaxation time of the starch component in the blends is shorter in comparison with values in unblended PIS, indicating that the molecular mobilities of the starch are also... 

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